The present invention relates to a process and a device in a chemicals recovery plant in a sulphate pulp mill.
From SE-B-8700549-2 there is known a process for treating green liquor, more particularly in such a way that the green liquor's content of particularly inorganic impurities and soot obtains better sedimentation and filtration properties and, owing to that, can be separated from the green liquor and accordingly removed from the chemicals cycle in a simpler and more effective way than before. This is achieved by adding to the non-clarified green liquor, while stirring quick lime comprising from 0.5 to 10%, preferably from 1 to 3% of the amount of quick lime necessary for complete causticizing of the green liquor.
According to SE-B-8700549-2 the quick lime is added either to a soda dissolver, in which melt from a soda recovery unit is dissolved in weak liquor, and from this to a mixing tank or directly to the mixing tank. From the mixing tank the green liquor formed is passed to a filter, from which solid particles are removed for dumping whereas clarified green liquor is passed to a lame slaker. From the lime slaker the mixture of lime and green liquor is passed to a causticizing tank from which the mixture of liquor and lime sludge formed is passed to a filter. The filtrate formed therein, white liquor, is passed to the digester house whereas the material filtered off, the lime sludge, is passed to a lime sludge silo. From this the lime sludge is passed to a washing filter from which the weak liquor formed is added to the above-mentioned soda dissolver whereas the lime sludge is passed into a lime kiln where it is burnt to lime. The quick lime is passed to the lime slaker as well as, according to the above, to either the soda dissolver or the mixing tank.